Flow boiling in high-aspect ratio mini- and micro-channels with FC-72 and ethanol: Experimental results and heat transfer correlation assessments

Flow boiling heat transfer in micro-channels using transparent heating was experimentally investigated. Three high-aspect-ratio (In the present study, for a channel cross section with a width W-in and a depth din, the channel aspect ratio alpha is considered to be high when MAX(W-in,d(in))/MIN(W-in,d(in)) > 10 or MIN(W-in,d(in))/MAX(W-in,d(in)) < 0.1.) rectangular micro-channels were used, the hydraulic diameters of which were 571 mu m, 762 mu m and 1454 mu m. Mass fluxes of 11.2 kg m(-2) s(-1), 22.4 kg m(-2) s(-1) and 44.8 kg m(-2) s(-1) and a wide range of heat fluxes were applied. Visualization results, thermography measurements and heat transfer characteristics of FC-72 and ethanol were obtained. Moreover, ten existing correlations for macro-, mini- and micro-channels were assessed. For ethanol, good predictions of three micro-channel correlations were achieved (MAE = 16.4-18.8%). However, all the correlations showed very high MAE for FC-72 (MAE = 80.7-641.3%). It is found that liquid properties and the unique high-aspect-ratio micro-channel geometry are crucial in developing a more accurate correlation. A modified correlation is proposed for FC-72 and ethanol with a MAE of 23.6%.